This invention relates to a three terminal transistor device and more particularly to a lateral heterojunction bipolar transistor (LHBT) having lateral emitter/base and collector/base heterojunctions fabricated by impurity induced disordering (IID) and also of a structure suitable as a hetero transverse junction (HTJ) laser.
Currently there is known in the art bipolar transistors which are for the most part vertical transistor structures which are junction dependent upon the epitaxial planar deposition of semiconductor layers, i.e., the p-n junctions of the device are formed at the interface of differently doped layers. Such junctions may also be formed as vertical heterojunctions via deposited heterostructure layers. Examples of such vertical transistors are found in U.S. Pat. Nos. 4,644,381 (right portion of FIG. 1 at "V"); 4,672,414; 4,728,616 and 4,620,210.
Further, efforts have been made to fabricate such transistors to have their junctions planar, i.e., positioned laterally from each other in the same layer or plane. Such an example is shown in the above mentioned U.S. Pat. No. 4,644,381 (left portion of FIG. 1 at "L") wherein a regrowth technique is employed to form a lateral heterojunction transistor having a heterojunction emitter and collector. Such a structure is complicated by a process of stopping epitaxial growth of layers B, C and D, performing a selective etching step down to a bottom deposited layer and thereafter continuing growth of layers E, F and I. Also, U.S. Pat. No. 4,639,275 to Holonyak, Jr. discloses in FIG. 5 a Schottky barrier FET which is a lateral transistor structure wherein device isolation is provided by IID regions 30 and 32.
In an article by Herbert Kroemer entitled, "Heterostructures for Everything: Device Principle of the 1980's?", Japanese Journal of Applied Physics, Vol. 20 (1981), Supplement 20-1, Proceedings of the 12th Conference of Solid State Devices, Tokyo, 1980, pp. 9-13, there is disclosed a lateral transistor device. In particular, on page 12 in FIG. 3 of this article, there is the suggestion of the introduction of energy bandgap variations to suppress carrier injection into portions of the base region where no injection is desired, indicating that this new important concept has powerful utility not apparently appreciated or widely recognized. FIG. 5, which is reproduced herein as FIG. 1, discloses a lateral pnp transistor 10 in I.sup.2 L as an example of incorporation of this concept. Transistor 10 includes, for example, consecutively deposited layers 12, 14 and 16 comprising respectively a wide bandgap material, a narrow bandgap material and a wide bandgap material. The transistor structure is fabricated by diffusion of a p-type impurity into regions 20 and 22, the former of higher concentration. The integrity of the deposited layers is maintained.
Kroemer recognized that a homostructure pnp design results in a poor transistor and further recognizes that heterostructure pnp design provides for confinement of injected holes in the true n base region 18 because the all narrow pnp structure formed in layer 14 is embedded between two wider bandgap layers 12 and 16. The two wider bandgap transistors formed in layers 14 and 16 are biased below their turn-on voltage, which is higher than that for the transistor of layer 14. Kroemer also recognizes that because of the small hole diffusion lengths in III/V compounds, the implementation will require submicron lengths for base region 18.
None of the foregoing transistor structures offer a lateral heterojunction bipolar transistor device with emitter and/or collector heterojunctions provided in an as-grown structure via simplified fabrication wherein the positions of the junctions as well as the selection of the base channel length can be accomplished without requiring any epitaxial regrowth technology.
Thus, it is an object of this invention to provide an improved lateral heterojunction bipolar transistor design in the III-V regime that permits the fabrication of laterally spaced heterojunctions without requiring regrowth techniques.